An optical disk recording and reading device includes a lens which focuses a laser light beam onto an optical disk while the disk is rotating. Focus and/or tracking actuators are used in optical disk recording and reading devices to control the position of the lens relative to the rotating disk. The actuators are necessary because of unavoidable warp of the disks, spindle errors, and other mechanical and optical imperfections.
Both focus and tracking of optical disks must continuously be maintained while the disks are recording and/or reading. Focus is controlled by adjusting the distance between the lens and the disk surface. Tracking is controlled by maintaining the lens at the correct radial position such that a single data track is read or written at a time. The motions of the actuator in the focus and tracking directions are controlled by a servo system.
Current actuators typically have a mechanical suspension system to control the motion of the actuator tangent to the disk, as well as three orthogonal rotations. This suspension system often includes a set of flexures. The flexures are typically designed to have high levels of mechanical damping in order to suppress actuator resonances, and thereby improve the overall functioning of the optical disk recording and reading device. Materials and configurations which have high mechanical damping often have low mechanical stability, i.e., the flexures creep and/or stress relax with time, particularly at elevated temperatures.
Alignment of the optical axis of the lens to the disk (i.e., lens tilt) must be maintained accurately for the system to function properly. The problem with the presently known and utilized optical actuator is that during the de-energized state, with time, the weight of the lens and lens holder causes the flexures to creep until the lens holder is resting on the base of the actuator. This contact, typically at an uncontrolled location, causes a moment on the flexures. This moment causes a torsional creep of the flexures, which results in a tilt motion being introduced to the lens and the lens holder. The lens tilt degrades the performance of the optical system, which consequently degrades the writing and reading reliability of the system.
FIG. 1 shows a prior art optical actuator 10 with a lens 12, a lens mount 14, an actuator base 16, and flexures 18. The flexures 18 are made of a high damping material, for example, viscoelastic plastic such as HYTREL elastomer (trademark of DUPONT). When the actuator 10 is in the de-energized state, the gravity creep with time would cause the lens mount 14 to contact the actuator base 16 at an uncontrolled position. This induces a moment about the x-axis, as shown in FIG. 1, which over time, induce a rotation of the lens mount 14 and the lens 12 about the x-axis. The rotation of the lens mount 14 and the lens 12 introduce an undesirable lens tilt error.